This invention relates to an improved cylindrical dampener cover used on an offset printing machine for supplying water to the plate cylinder. More particularly, the invention relates to a dampener roll cover for use in an offset printing machine prepared by knitting or weaving yarns into the cover that are shrinkable by water and are used as inlay yarns, with hydrophilic yarns as pile yarns, and any natural or man made yarns as ground yarns.
Prior art dampener roll covers used to supply water to the plate cylinder were prepared by fabricating a cloth made by knitting or weaving cotton into a cylindrical shape, mounting it onto a dampener roll, and stretching it by pulling the opposite ends of the cylindrically shaped cloth before use. Difficulties encountered in this technique are that the covering fabric is apt to be loosened by centrifugal force during the rotation of the roll, causing the supply of water to the plate cylinder to become uneven due to uneven stretching of the fabric. This causes frequent interruptions of the printing operation in order to replace the covering fabric with a new cover or to try to restretch the old one. This eventually results in a reduction of the efficiency of the printing operation, adding additional costs of material and labor.
In U.S. Pat. No. 3,242,554, it is disclosed that dampener roll covers can be made from water-shrinkable fabrics. These fabrics are made into a cylindrical cover, mounted on a dampener roll and immersed in water to shrink the cover on the roll. However, these particular water-shrinkable fabrics must first be wet-stretched and dried prior to use, and they have a limited degree of stretch, and then shrink by less than the original stretching when wet. This particular covering has drawbacks, because with the limited shrinkage, the cover must be measured to the rolls on which they are to be used and the same size cover cannot be used on rolls that have been reground, as they must be because of use.
Additionally, U.S. Pat. No. 3,926,701 discloses a covering fabric for a dampener roll, which is comprised of yarn capable of shrinking by the action of water. However, the shrinkable yarns used therein are employed as the ground yarn of the covering with hydrophilic yarns used as the pile yarn. In mounting the covering fabric of this invention onto a dampener roll, the roll covered with the fabric is immersed in water, often warm water, and the ground yarns of the covering fabric shrinks to closely fix the covering fabric to the dampener roll. In addition, because shrinkage occurs on the dampener cover in the lengthwise direction, when mounting, sufficient fabric must be used in order to accommodate the lengthwise shrinkage of the dampener cover to cover the dampener roll. It is therefore difficult, if not impossible, to be able to calculate the correct length of the covering fabric that should be used. Thus, one must use an excess of material to insure an adequate fit. Because of the aforementioned, furthermore there is a loss that arises with respect to the material and man hours that may be lost due to the material that may have to be removed after shrinkage of the covered fabric to the dampener roll.
There are other additional drawbacks in using the shrinkable yarns as the ground yarn, namely, the yarns when used as the ground yarn tend to make the cover very stiff; difficult to mount on a dampener roll; harder to remove from the roll and at larger diameters can create sufficient force upon the dampener roll to cause damage to the roll.
The present invention has succeeded where others have failed in obtaining an excellent covering fabric for a dampener roll without the drawbacks encountered with either the conventional structured covers or by the prior art water-shrinkable covers.